In battery manufacture material which eventually forms the battery plates undergoes a number of treatments, one of which is impregnation into the battery plates of selected material such as sodium nitrate. A further step in the process of preparing battery plate material is a washing of the impregnated plates so as to remove excess material from the plates. This results in the washing medium carrying away this excess material, thus increasing the concentration of that material in the washing medium. Due to existing environmental regulations this used wash medium cannot be exhausted into rivers or otherwise into the environment, and must be treated to remove at least predetermined levels of the impurities, and in some instances to remove the impurities entirely. Such waste water treatment is ancillary to the main purpose of preparation of battery plate material and therefore it is desirable to decrease the cost impact of this waste water treatment. Prior to impact of environmental regulations the wash medium was used only once. As a result, the impurity concentration, although too low to justify economic impurity recovery, did prevent this once used wash medium from being used for human consumption.
One useful technique in reducing the quantities of a washing medium employed is that of employing successive washes with washing media of sequentially decreasing levels of impurities so that, by the time of the last wash in the sequence, the material being washed is washed with a washing medium having relatively low level impurities. To make such a sequential washing operation successful, however, it is essential that the several washing media employed be maintained separate from one another, for if a relatively impure washing medium is allowed to mix with a relatively purer washing medium, any advantages which flow from the sequential washing step is reduced or eliminated. Such a sequential washing operation requires first that a wash tank, containing an object to be washed, be filled from a source of relatively impure washing media, a washing operation then takes place, at the conclusion of which the wash tank is drained, the drained fluid going back to the original source; the wash tank is then filled from a source of relatively purer washing medium and the wash and drain operation are repeated. This sequential filling, washing and draining takes place from the various different sources of washing media, having progressively lower levels of impurities, until the material being washed is washed with the purest washing medium available. The referred to disadvantageous mixing could occur, if the wash tank were not completely drained before it was again filled. Although use of a level sensor to signal draining of a wash tank might be considered, such a device is not usable, for practical reasons. The particular impurities which battery making operation requires, renders the available level sensors unusable, either because the impurities in the washing media would quickly clog such a level sensor and thus render it unusable, or because the particular level sensors are not suited to the environment in which battery making occurs, constituting a heavy industrial process, including relatively uncontrolled temperatures, electrical noise, etc.
As the washing process continues the impurity concentration of each of wash media increases. The process must be terminated and the wash media limited in impurity concentration in order to ensure that effective washing is possible. Desirably, however, the termination should only be temporary, the aggregate impurity level of each of the various washing media should be reduced and the sequence begun anew with as little impact as possible on the actual wash steps. Unfortunately the washing, termination and aggregate impurity reduction cannot operate on a strictly timed basis since the rate at which impurities enter the wash media fluctuates with time and so operating on a fixed time sequence would, at times terminate too early (when the aggregate impurity level was still low enough for effective washing) and at times terminate too late when aggregate impurity level had risen to the point that effective washing was no longer feasible.
Solution of these simultaneous requirements also must take into account that the washing step in the manufacturing process is one of a series of time sequential process steps which may be carried out on a plurality (N, where N is an integer of 1-10) of "lines" simultaneously although not synchronously. Accordingly therefore, the demands on the various sources can vary unpredictably over quite a wide range (for example, from simultaneously draining N wash tanks to a common tank to, at other times, simultaneously filling N wash tanks from a common tank). These sources (including the tanks) must be capable of such operation without substantial variation in rate of filling and draining since, as will be seen, the time to fill is used as the only indicator that a prior drain operation was complete.
It is therefore, one object of the present invention to provide a fluid handling system which is capable of meeting the requirements imposed by the necessity for washing battery plate material in the course of battery making, which is suitable for such an environment, but which at the same time minimizes the extent to which washing media is exhausted. It is another object of the present invention to provide such a fluid handling system which is completely automatic in operation, and which both minimizes the extent to which the different washing media are mixed in the course of sequential washing operations, and at the same time is capable of both detecting and recovering from a condition in which unwanted mixing of the different washing media is detected. It is a further object of the invention to provide such a fluid handling system which is capable of both sequentially filling and draining from 1 to N wash tanks from various tanks or sources of washing media or differing impurity concentrations, but which is also capable of sequentially cascading (transferring) the washing media employed from tank-to-tank when the impurity concentration of the tank of lowest concentration reaches a threshold, and effecting the cascade with minimum impact on the various wash operations, then in process.